Variable speed drive

ABSTRACT

Systems and methods for improved VSDs are provided. One embodiment relates to an apparatus for common mode and differential mode filtering for motor or compressor bearing protection when operating with VSDs, including conducted EMI/RFI input power mains mitigation. Another embodiment relates to a method to extend the synchronous operation of an Active Converter to the AC mains voltage during complete line dropout. Another embodiment relates to an Active Converter-based Variable Speed Drive system with Improved Full Speed Efficiency.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation in part of U.S. patent applicationSer. No. 11/978,939, filed Oct. 30, 2007, entitled VARIABLE SPEED DRIVE,which is hereby incorporated by reference.

BACKGROUND

The present application relates generally to variable speed drives. Theapplication relates more specifically to an input filter for a variablespeed drive to filter line to ground voltages and reduce high frequencydistortion in the converter stage.

A variable speed drive (VSD) for heating, ventilation, air-conditioningand refrigeration (HVAC&R) applications typically includes a rectifieror converter, a DC link, and an inverter. The rectifier or converterconverts the fixed line frequency, fixed line voltage AC power from anAC power source into DC power. The DC link filters the DC power from theconverter and typically contains a large amount of electricalcapacitance. Finally, the inverter is connected in parallel with the DClink and converts the DC power from the DC link into a variablefrequency, variable voltage AC power.

If a high frequency distortion of the line to ground voltage (V_(lg)) ispresent at the input of the VSD, the voltage across the input devices(V_(ce)) can become distorted. The distortion of V_(ce) may cause highvoltage transients across the input devices of the VSD in addition tothe normal input voltage to the VSD. If the high voltage transientscombined with the input voltage exceed the maximum permissible ratedvoltage for an input device of the VSD, the device may fail. A failurecan occur when the input devices are not switching or operating, but arestill connected to the input lines.

The traditional solution to the problem of high frequency distortion ofV_(lg) is to provide a galvanically isolated disconnect, e.g., acontactor, between the VSD and AC power source. The galvanicallyisolated disconnect isolates the input devices from the high frequencydistortion of V_(lg), when the input devices are not switching. Thegalvanically isolated disconnect increases the cost, size, complexityand weight of the VSD. Another solution to mitigate high frequencydistortion of V_(lg) may be to use input devices rated at a highervoltage. Devices with higher voltage ratings, however, increase the costof the VSD and may reduce its efficiency.

What is needed is a system and/or method that satisfy one or more ofthese needs or provides other advantageous features. The presentapplication is directed to both VSDs that incorporate an activeconverter type AC to DC converter topology and VSDs utilizingconventional AC to DC rectifier converters.

Other features and advantages will be made apparent from the presentspecification. The teachings disclosed extend to those embodiments thatfall within the scope of the claims, regardless of whether theyaccomplish one or more of the aforementioned needs.

SUMMARY

The present invention is directed to a circuit for three-phase PulseWidth Modulated (PWM) VSDs, and preferably for PWM VSDs having activeconverter topologies.

In one embodiment, a variable speed drive system is disclosed. Thevariable speed drive system is arranged to receive an input AC power ata fixed AC input voltage and frequency and provide an output AC power ata variable voltage and variable frequency. The variable speed driveincludes a converter stage connected to a three phase AC power sourceproviding the input AC voltage. The converter stage is configured toconvert the input AC voltage to a boosted DC voltage. A DC link isconnected to the converter stage. the DC link is configured to filterand store the boosted DC voltage from the converter stage. An inverterstage is connected to the DC link. the inverter stage is configured toconvert the boosted DC voltage from the DC link into the output AC powerhaving the variable voltage and the variable frequency. The variablespeed drive includes an input filter with a three-phase input capacitorbank including three capacitors connected in a wye configuration. Eachrespective capacitor of the three capacitors is connected between onephase of the three phase AC power source at a first end of therespective capacitor, and a common point at a second end of therespective capacitor. A grounding capacitor is connected between thecommon point and earth ground. The three-phase input capacitor bank isconfigured to filter line to ground voltages to reduce or substantiallyeliminate high frequency distortion across the converter stage.

In another embodiment, an input filter is provided for reducing oreliminating high frequency distortion of line to ground voltages. Theinput filter includes a three-phase inductor having three windings,wherein each winding of the three-phase inductor further includes acenter tap. The center tap divides each winding of the three-phaseinductor into a pair of inductor sections. A three-phase input capacitorbank includes three capacitors connected in a wye configuration to thethree center taps at one end, and to a common point at the opposite end.A grounding capacitor is connected between the common point and earthground. The three-phase input capacitor bank is configured to filterline to ground voltages to substantially eliminate high frequencyvoltage transients across an input of a converter stage.

One advantage is to reduce the common mode and differential modecurrents associated with conducted electromagnetic interference andradio frequency interference present at the AC power source as a resultof the operation of the VSD.

A second advantage is the integral bypass active converter configurationmay be utilized for VSD controlled systems that operate at a maximumfrequency & voltage equal to the power line mains frequency supplied tothe VSD. Contactor bypass eliminates the losses associated with the VSDwhen the system is required to operate at maximum frequency.

Another advantage is a ground fault protection system in an activeconverter for instantaneously interrupting a ground fault at an inputphase of the active converter, using reverse blocking IGBTs tocontrollably switch off fault current in response to a sensed fault.

Still another advantage is improved cooling and reduced size, weight andcost of the inductor.

Alternative exemplary embodiments relate to other features andcombinations of features as may be generally recited in the claims.

BRIEF DESCRIPTION OF THE FIGURES

The application will become more fully understood from the followingdetailed description, taken in conjunction with the accompanyingfigures, wherein like reference numerals refer to like elements.

FIGS. 1A and 1B show schematically embodiments of general systemconfigurations.

FIGS. 2A and 2B show schematically embodiments of variable speed drives.

FIG. 3 shows schematically an embodiment of a vapor compression system.

FIG. 4 shows schematically a common mode and differential mode inputfilter using a four- or five-legged inductor.

FIG. 5 shows a one-quarter section view of a five-legged inductor core.

FIG. 6 shows a cross-sectional view of an embodiment of a five-leggedinductor core.

FIG. 7 shows a schematically an alternate embodiment a variable speeddrive.

FIG. 8 shows a cross-sectional view of an embodiment of a four-leggedinductor core.

FIG. 9 shows a block diagram of an embodiment of active converter mainsangle retention control.

FIG. 10 shows schematically another embodiment of a variable speeddrive.

FIGS. 11 and 12 show embodiments of flow control diagrams of controlalgorithms for a variable speed drive.

FIG. 13 shows an embodiment of an inverse parallel connection of tworeverse-blocking IGBTs.

FIG. 14 shows a prior art conventional 3-phase active converter module.

FIG. 15 shows a plan view of an embodiment of a plastic cooler.

FIG. 16 shows cross-sectional view of the plastic cooler of FIG. 15through line 3-3.

FIG. 18 shows a cross-sectional view of the plastic cooler of FIG. 15through line 4-4.

FIG. 17 shows a plan view of the well and O-ring of the plastic coolerof FIG. 15.

FIG. 19 shows a plan view of a second embodiment of the well and O-ringof the plastic cooler of FIG. 15.

FIG. 20 shows an exploded view of an embodiment of a film capacitor.

FIG. 22 shows an embodiment of a five-legged liquid-cooled inductor.

FIG. 21 shows a cross-section of an embodiment of a five-legged core,liquid cooled inductor.

FIG. 23 shows a CFD analysis of the five-legged liquid-cooled inductorof FIG. 21.

FIG. 24 shows an exemplary embodiment of a common mode capacitor circuitand active inverter module.

FIG. 25 shows a line-to-ground voltage waveform V_(lg) for a VSD circuithaving high-frequency distortion.

FIG. 26 shows the line-to-ground voltage waveform V_(lg) of FIG. 25modified to include a common mode capacitor.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Before turning to the figures which illustrate the exemplary embodimentsin detail, it should be understood that the application is not limitedto the details or methodology set forth in the following description orillustrated in the figures. It should also be understood that thephraseology and terminology employed herein is for the purpose ofdescription only and should not be regarded as limiting.

FIGS. 1A and 1B show general system configurations. An AC power source102 supplies a variable speed drive (VSD) 104, which powers a motor 106(see FIG. 1A) or motors 106 (see FIG. 1B). The motor(s) 106 can be usedto drive a corresponding compressor of a vapor compression system (seegenerally, FIG. 3). The AC power source 102 provides single phase ormulti-phase (e.g., three phase), fixed voltage, and fixed frequency ACpower to the VSD 104 from an AC power grid or distribution system thatis present at a site. The AC power source 102 can supply an AC voltageor line voltage of 200 V, 230 V, 380 V, 460 V, or 600 V, at a linefrequency of 50 Hz or 60 Hz, to the VSD 104 depending on thecorresponding AC power grid.

The VSD 104 receives AC power having a particular fixed line voltage andfixed line frequency from the AC power source 102 and provides AC powerto the motor(s) 106 at a desired voltage and desired frequency, both ofwhich can be varied to satisfy particular requirements. The VSD 104 canprovide AC power to the motor(s) 106 having higher voltages andfrequencies and lower voltages and frequencies than the rated voltageand frequency of the motor(s) 106. In another embodiment, the VSD 104may again provide higher and lower frequencies but only the same orlower voltages than the rated voltage and frequency of the motor(s) 106.The motor(s) 106 can be an induction motor switched reluctance motor orpermanent magnet motor, but can include any type of motor that iscapable of being operated at variable speeds.

FIGS. 2A and 2B show different embodiments of the VSD 104. The VSD 104can have three stages: a converter stage 202, a DC link stage 204 and anoutput stage having one inverter 206 (see FIG. 2A) or a plurality ofinverters 206 (see FIG. 2B). The converter 202 converts the fixed linefrequency, fixed line voltage AC power from the AC power source 102 intoDC power. The DC link 204 filters the DC power from the converter 202and provides energy storage components. The DC link 204 can be composedof capacitors, inductors, or a combination thereof, which are passivedevices that exhibit high reliability rates and very low failure rates.Finally, in the embodiment of FIG. 2A, the inverter 206 converts the DCpower from the DC link 204 into variable frequency, variable voltage ACpower for the motor 106 and, in the embodiment of FIG. 2B, the inverters206 are connected in parallel on the DC link 204 and each inverter 206converts the DC power from the DC link 204 into a variable frequency,variable voltage AC power for a corresponding motor 106. The inverter(s)206 can be a power module that can include power transistors, insulatedgate bipolar transistor (IGBT) power switches and inverse diodesinterconnected with wire bond technology. Furthermore, it is to beunderstood that the DC link 204 and the inverter(s) 206 of the VSD 104can incorporate different components from those discussed above so longas the DC link 204 and inverter(s) 206 of the VSD 104 can provide themotors 106 with appropriate output voltages and frequencies.

With regard to FIGS. 1B and 2B, the inverters 206 can be jointlycontrolled by a control system such that each inverter 206 provides ACpower at the same desired voltage and frequency to corresponding motorsbased on a common control signal or control instruction provided to eachof the inverters 206. In another embodiment, the inverters 206 can beindividually controlled by a control system to permit each inverter 206to provide AC power at different desired voltages and frequencies tocorresponding motors 106 based on the separate control signals orcontrol instructions provided to each inverter 206. Individuallycontrolling inverters 206 permits the inverters 206 of the VSD 104 tomore effectively satisfy motor 106 and system demands and loadsindependent of the requirements of other motors 106 and systemsconnected to other inverters 206. For example, one inverter 206 can beproviding full power to a motor 106, while another inverter 206 isproviding half power to another motor 106. The control of the inverters206 in either embodiment can be by a control panel or other suitablecontrol device.

For each motor 106 to be powered by the VSD 104, there is acorresponding inverter 206 in the output stage of the VSD 104. Thenumber of motors 106 that can be powered by the VSD 104 is dependentupon the number of inverters 206 that are incorporated into the VSD 104.In one embodiment, there can be either 2 or 3 inverters 206 incorporatedin the VSD 104 that are connected in parallel to the DC link 204 andused for powering a corresponding motor 106. While the VSD 104 can havebetween 2 and 3 inverters 206, it is to be understood that more than 3inverters 206 can be used so long as the DC link 204 can provide andmaintain the appropriate DC voltage to each of the inverters 206.

FIG. 3 shows an embodiment of a vapor compression system using thesystem configuration and VSD 104 of FIGS. 1A and 2A. As shown in FIG. 3,the vapor compression system 300 includes a compressor 302, a condenser304, a liquid chiller or evaporator 306 and a control panel 308. Thecompressor 302 is driven by motor 106 that is powered by VSD 104. TheVSD 104 receives AC power having a particular fixed line voltage andfixed line frequency from AC power source 102 and provides AC power tothe motor 106 at desired voltages and desired frequencies, both of whichcan be varied to satisfy particular requirements. The control panel 308can include a variety of different components such as an analog todigital (A/D) converter, a microprocessor, a non-volatile memory, and aninterface board, to control operation of the vapor compression system300. The control panel 308 can also be used to control the operation ofthe VSD 104, and the motor 106.

Compressor 302 compresses a refrigerant vapor and delivers the vapor tothe condenser 304 through a discharge line. The compressor 302 can beany suitable type of compressor, e.g., screw compressor, centrifugalcompressor, reciprocating compressor, scroll compressor, etc. Therefrigerant vapor delivered by the compressor 302 to the condenser 304enters into a heat exchange relationship with a fluid, e.g., air orwater, and undergoes a phase change to a refrigerant liquid as a resultof the heat exchange relationship with the fluid. The condensed liquidrefrigerant from condenser 304 flows through an expansion device (notshown) to the evaporator 306.

The evaporator 306 can include connections for a supply line and areturn line of a cooling load. A secondary liquid or process fluid,e.g., water, ethylene glycol, calcium chloride brine or sodium chloridebrine, travels into the evaporator 306 via return line and exits theevaporator 306 via supply line. The liquid refrigerant in the evaporator306 enters into a heat exchange relationship with the secondary liquidto lower the temperature of the secondary liquid. The refrigerant liquidin the evaporator 306 undergoes a phase change to a refrigerant vapor asa result of the heat exchange relationship with the secondary liquid.The vapor refrigerant in the evaporator 306 exits the evaporator 306 andreturns to the compressor 302 by a suction line to complete the cycle.It is to be understood that any suitable configuration of condenser 304and evaporator 306 can be used in the system 300, provided that theappropriate phase change of the refrigerant in the condenser 304 andevaporator 306 is obtained.

Furthermore, while FIG. 3 illustrates the vapor compression system 300as having one compressor connected in a single refrigerant circuit, itis to be understood that the system 300 can have multiple compressors,powered by a single VSD as shown in FIGS. 1B and 2B or multiple VSDconnected into each of one or more refrigerant circuits.

Referring next to FIG. 4, there is a schematic diagram of elements of aninput filter 10 shown. EMI/RFI sources 40 generated by the activeconverter 202 can be filtered ahead of the converter 202 by splitting athree-phase AC input inductor 16 into a line-side inductor 26 andload-side inductor 28 per phase. The line-side inductors 26 andload-side inductors 28 are connected by inductor tap portions 18. Acapacitive three-phase filter element 20 is wye-connected between theinductor tap portions 18. An optional earth connection 22 may beconnected to a common point 21 of the wye-connected filter element 20.The earth connection 22 may alternately include a grounding capacitor23. The line- and load-side inductors 26 and 28, respectively, and thecapacitive filter element 20 are designed with inductance andcapacitance values to provide a roll off of the EMI/RFI sources—i.e.,high frequency switching components of the input current conducted bythe converter 202. The input filter 10 provides a high impedance via thedifferential mode inductive components of inductances 26 and 28 and alow impedance via the three-phase wye connected capacitance 20 to theEMI/RFI sources, while passing the fundamental component of the powercurrent, e.g., 60 Hz, through the network with minimal impedance. Byutilizing a four- or five-legged (⅘) input inductor 16, a common modeinductive component is formed via inductances 26 and 28 and togetherwith the optional earth connection 22 or the grounding capacitor 23,increases the capacity of the filter 10 to prevent common mode currentgenerated by the converter 202 from flowing into the “mains” or AC powersource 102. The wye-connection point 21 of the input filter 10 may bedirectly earthed or alternately earthed through a separate capacitor 23to provide greater shunting of high-frequency currents to earth. In oneembodiment, the inductor 16 may be provided with low inter-windingcapacitance.

Line-side inductors 26 provide impedance at a predetermined switchingfrequency of the VSD 104 between the wye-connected capacitors 20 and theAC power source 102. The impedance of the line-side inductors 26 can bedesigned to allow the wye-connected capacitors 20 to be more effectivethan a system with no significant impedance between the input AC powersource 102 and the VSD 104. Inductors 26 also provide high-frequencyimpedance in the reverse direction, to restrict the flow ofhigh-frequency current from the converter 202 to the AC power source102. Thus the inductors 26 restrict or limit high frequency current fromreflecting back to the AC power source 102.

Inductors 28 provide impedance between the capacitors 20 and the inputto the VSD 104. Inductors 28 provide high impedance between the AC powersource 102 and the active converter 202 portion of the VSD 104.Alternately, if the VSD 104 is a VSD with a passive rectifier orconverter, the impedance of inductors 28 isolates the VSD 104 from theinput AC power source 102 and reduces high frequency emissions conductedby to the AC power source 102 from the VSD 104.

The wye-connected capacitor bank 20 provides low impedance between phaseconductors A, B & C for at least one switching frequency of the VSD 104,and provides low impedance for differential mode current flow. Thewye-connected capacitor bank 20 also provides a low impedance path forflow of at least one switching frequency to an earth ground connection22, assuming that an earth ground connection is provided, for reducingcommon mode current flow.

In one embodiment, the common mode input filter 10 may be implementedusing either a four-legged AC inductor 516′ (see, e.g., FIG. 8, orfive-legged AC inductor 516 (see e.g., FIGS. 5 and 6), collectivelyreferred to as ⅘ inductor, applied to the input of the VSD 104 withactive converter technology. Conventional filters employ three-leggedinductors to provide power factor and harmonic input current control.The ⅘ inductor 516 provides both common mode and differential modeinductance. FIGS. 5 and 6 show a five-legged inductor 516, whichprovides more geometric symmetry in a three-phase power system. Thecommon mode inductance is generated by providing a magnetic flux path504, indicated by arrow 502. The flux path 504 can be in magneticcommunication with three core legs 510, 512 and 514, each of which areconnected to one of the phases in the three phase input power 102. Theflux path 504 can be a continuous, magnetically permeable magnetic loopthat surrounds the inner three core legs 510, 512 and 514. Each of thecore legs 510, 512 and 514 can have a coil winding or inductor 26 (see,e.g., FIG. 4) wrapped around substantially the entire surface area ofthe respective core leg 510, 512 and 514. The direction of the magneticflux in the flux path can be dependent upon the direction and magnitudeof the currents in the coil windings, and are therefore shown as flowingin either direction, although in practice, the magnetic flux may flow inone direction or another about the about the periphery of the inductor516. The common mode magnetic flux is induced by electrical currentsthat are common to all three inductor coils 26. The common mode fluxpath 504 can only be excited by common mode current components flowingthrough the inductor coils. In one embodiment, inductor 516 can have aliquid-cooled core to improved heat dissipation and increase the powercapacity of the inductor 516.

Referring to FIG. 6, the five-legged inductor 516 can have air gaps 520that are inserted in the legs 510, 512 and 514 to prevent coresaturation and increase the working flux density range of the inductor516. In the inductor 516, an air gap 520 can be arranged between thehorizontal sections of the flux path 504. Two air gaps 520 can also beinserted intermediately in each of the core legs 510, 512 and 514, tobreak up each core leg 510, 512 and 514, into three discrete segments.Other air gap configurations may be used to achieve the same result.

Referring next to FIG. 7, another embodiment of a VSD with an outputfilter and a common mode/differential mode input filter circuit isshown. The EMI/RFI input filter as described with respect to FIG. 4,above, is connected at the input of the converter 202, and performs thesame filtering functions as described with respect to FIG. 4. Theaddition of the input filter with an inductor 16 at the input to the VSD104 can effectively provide a high-impedance circuit between the ACpower source 102 and the VSD 104. To provide a low impedance path forcommon mode current flow, a three-phase wye connected capacitor bank 30including three common mode capacitors 32 are connected between theVSD's motor connection terminal 38, and earth ground 22. The capacitorbank 30 is equivalent to a short circuit—i.e., low impedance—at highfrequency, effectively earthing or removing the destructive highfrequency AC components present on the three VSD output terminals 34 andshunting the destructive AC components from reaching the motor or othertype of load connected to the VSD, thus filtering out currents resultingfrom common mode voltages. The capacitor bank 30 allows high-frequencyAC components to bypass the parasitic capacitive earthing elements ofthe motor and eliminates bearing damage caused by common mode voltagesand currents.

The inverter output terminals 34 feed a second filter arrangement thatincludes a three phase inductor 36 connected in series with the outputterminals 38, which are connected to the system load, e.g., a motor 106.Three-phase capacitor bank 30 is wye-connected to the output powerphases, L1, L2 and L3, between the load side of the three phase inductor36, providing a low impedance path for the differential mode current toflow among the capacitor bank 42. The combination of the secondthree-phase capacitor bank wye-connected at the load side of the threephase inductor 36 provides an L-C differential mode output filter. Bycombining the common mode filter capacitor bank 20, with the L-Cdifferential mode inductor 36 and capacitor bank 30 both of thedestructive conditions, i.e., common mode and differential modecurrents, are prevented from reaching a load that is powered by the VSD104.

Referring next to FIG. 9, a mains phase angle (MPA) control system 900is shown. The control system 900 provides retention of the phase angleinformation for the AC input source or mains voltage 102 during inputvoltage dropout. The mains voltage 102 is applied to a squaringamplifier 901 to generate a substantially rectangular output signal fromthe ac input signal. The output of the squaring amplifier issimultaneously input to a pair of phase-locked-loops (PPLs) 902, 904.The first PLL 902 has a phase detector 918 for comparing a referencesignal SIG with a comparison signal COMP for detecting when the phase ofthe input signal is out of phase lock with a voltage controlledoscillator (VCO) 922. If the phase detector 918 detects that the twoinputs SIG and COMP are out of phase lock, a reset signal is output fromterminal LD of the phase detector 918 to a 1-shot circuit 924. The1-shot circuit 924 generates a narrow pulse input to a sample and hold(S&H) circuit 910. The output error signal of phase detector 918 ispassed through a lag-lead filter circuit 906 to VCO 922. The outputsignal from the VCO 922 is then input to a divide-by-N circuit 926. Thedivide-by-N circuit 926 provides the comparison signal which is appliedto the COMP terminal of the phase detector 918, and also outputs asecond signal indicating the mains voltage d-q axis digital angle outputfast response 928.

The second PLL 904 circuit is similarly configured as PLL 902 with phasedetector 920 comparing the input reference signal SIG with a comparisonsignal COMP, and outputting an error signal to lag-lead filter 908. Thelag-lead filter 908 has S&H circuit 914 controlled by 1-shot circuit 930and analog switch 916. The lag-lead filter 908 can have a low cutofffrequency. The VCO 932 is input to a divide-by-N circuit 934, whichgenerates the COMP signal input to the phase detector 920, and outputs asecond signal indicating the mains voltage d-q axis digital angle outputslow response 936.

The control system 900 may be used to retain synchronous operation of aVSD 104 with an active converter 202 to reduce current distortion andeliminate regeneration of energy upon reapplication of the AC inputmains voltage 102—for providing extended ride-through capability in theVSD 104. Use of the two PLLs 902, 904 enables the control system 900 tomaximize the ability of the active converter 202 to retain the bestavailable knowledge of the line-to-line voltage phase angle at the ACinput source 102 under all conditions. The first PLL 902 lag-lead filter906 has a relatively high filter cutoff frequency and small valueintegrating capacitor C1. Filter 906 provides the active converter 202the capability for fast and accurate phase angle tracking under normalconverter operating conditions. The filter 906 components includeresistor R1, resistor R2 and capacitor C1. In one embodiment, thecomponent value for resistor R1 may be 43K ohms, for resistor R2, 120Kohms, and for capacitor C1, 0.47 uF, although the lag-lead filter 906components R1, R2 and C1 may be varied to adjust the desired cutofffrequency of the filter 906. The second PLL 904 lag-lead filter 908 hasa low cutoff frequency, a large value integrating capacitor C2, andresistors R3 and R4. The low cutoff frequency provides the lag-leadfilter 908 with the capability for storing the angle of the mainsvoltage in the feedback loop of the PLL during mains interruption. Inone embodiment, the typical component values for R3, R4 and C2 may be510K ohms, 68K ohms and 2.2 uF, respectively. To increase the capabilityto retain mains or AC power source phase angle information during apower interruption, each PLL feedback loop 906, 908 includes a sampleand hold (S&H) circuit 910, 914 respectively, and analog switchintegrated circuits 912, 916 respectively. The S&H circuits 910, 914with analog switches 912, 916 hold the stored charge on the integratingcapacitors C1, C2 within each lag-lead filter 906, 908, and prevent thedischarge of the capacitors C1, C2 through leakage to the output of thephase detectors. The component sizing of the ratio R3/R4 is alsoselected to minimize step change in the voltage fed to the VoltageControlled Oscillator 932 when the analog switch 916 is transitioned.

The position of each analog switch 912, 916 is controlled by the sensingof the total loss of the mains or AC power source voltage 102 via themains voltage detector (or mains present) circuitry. The sample and holdcircuits 910, 914 are controlled by the out of phase lock detectorsincorporated into each phase detector. The VCO outputs are fed to divideby n bit counters 926, 934, where n is chosen as a function of theresolution of the phase angle required in the specific application. Thecounter outputs are then fed back into the second input (denoted COMP)of each phase detector 918, 920 to form a closed loop. The counteroutputs are also used to provide a digital word 928, 936 representativeof the mains or AC power source phase angle. The digital words 928, 936then govern the d-q angle output during mains or AC power sourceinterruption. Selection of timing to transition the phase angleinformation is a function of the specific application but can bedetermined using the mains voltage detector (mains present) circuitry.In one embodiment the PLLs 902, 904 may be implemented using a 74HC7046integrated circuit manufactured by Phillips Semiconductor Corp. The74HC7046 integrated circuit includes a state machine type phase detectorwith out of phase lock detector and a Voltage Controlled Oscillator. Thecircuit design allows a power interruption of up to one second induration without incurring phase error beyond a specified angle underworst-case conditions.

Referring next to FIG. 10, a VSD 104 includes a three-phase line reactor402 connected to the AC voltage source 102 through protective devicessuch as fuses 10 or a circuit breaker. The line reactor 402 enablescurrent limiting at the input of the active converter 202 and allows forthe generation of the boosted DC link voltage. An output LC filter 404is connected to the output of the inverter 206 to filter the outputwaveform and attenuate electrical noise and harmonics associated withthe inverter 206 output waveform. The LC filter 404 is connected inseries with the inverter 206 and, e.g., the motor 106 (see, e.g., FIG.1A). A three phase bypass contactor 400 is connected in parallel withthe VSD 104, from the downstream side of the protective devices 10 tothe output of the LC filter 404. The use of an active converter 202provides fast active control of the voltage at the DC link 204. Theactive converter 202 provides extended ride-through capability,operating capability over a universal input voltage, and the capabilityof programming the AC output voltage magnitude independently of theinput line voltage magnitude. Using the active converter 202, thevoltage at the DC link 204 is precisely and quickly controlled. Thus,the AC output voltage of the VSD 104 is also precisely and quicklycontrolled. Filter 404 is connected at the output of the VSD 104 toprovide sinusoidal output voltage to the motor 106. A bypass contactor400 is incorporated within the VSD 104 to provide direct,across-the-line operation of a motor 106 at full speed. The integralbypass contactor 400 can be enabled and disabled if properly applied tothe VSD 104 equipped with an active converter 202. The configurationshown in FIG. 10 permits continuous operation of the VSD 104 at either50/60 Hz mains of AC power source operation or reduced frequencyoperation, without interrupting the operation of the motor 106 andcompressor 302, when switching from VSD operating mode toacross-the-line operating mode. Precisely controlling the VSD outputvoltage, frequency and phase of the frequency in synchronization withthe input voltage, phase and frequency of the AC voltage source 102provides a smooth, transparent transfer of the electrical load, betweenacross-the-line (i.e., full mains or AC power source voltages andfrequency) operation, and VSD-controlled operation, in both directions.The smooth, transparent load transfer eliminates torque excursionsbeyond the required torque demanded by the load. The smoothload-transfer capability eliminates driveline shock that is typicallyassociated with transferring the power feed from VSD to mains or ACpower source. As a result, a reduced-size contactor may be used totransfer the load, and inrush current is eliminated, regardless of themode in which the VSD 104 is operating.

The power loss of the VSD 104 at full-speed operation can be reduced oreliminated by bypassing the VSD 104. Normal losses associated with aconventional VSD typically range from 2 to 3%, and the losses may rangeas high as 4 to 5% for a VSD that employs an active converter 202.Application of the VSD 104 with the integral bypass contactor 400 forpowering an HVAC chiller system provides a significant increase in thefull load KW/TR rating of the chiller system. Thus, a system with a VSD104 equipped with an integral bypass contactor 400 provides anefficiency rating comparable with that of a system that is not equippedwith a VSD 104, resulting in substantial energy savings. The energysavings and higher efficiency ratings are achievable even during periodswhen the full capacity of the system is required. By utilizing a VSD 104having an active converter 202 and integral bypass contactor 400, acontactor that may typically be used for pre-charge means in existingactive converter VSDs may now applied to eliminate power lossesassociated with the VSD 104 during full speed operation. The system ofFIG. 10 thus provides, for about the same cost, a VSD-equipped systemhaving greater full-speed and full KW/TR efficiency, when compared withconventional systems, i.e., systems having a VSD with an activeconverter, and without an integral bypass contactor.

Referring to FIG. 10, three input fuses 10 are included to interruptovercurrent at the AC voltage source 102. On a per-phase basis, theparameters that must be sensed to implement the control scheme are theinput voltage VIN, the DC link voltage VDC, the VSD 104 output currentIVSD, and the motor current IMTR. A circuit breaker or disconnect switch(not shown) may be included at the input connection to the AC voltagesource 102. The fuses 502 may be used in lieu of or in addition to acircuit breaker for overcurrent and fault protection.

To provide a smooth transition from VSD to mains or AC power source orvice versa, three conditions must be present, as follows: 1) the inputRMS voltage VIN to the VSD 104 must equal the RMS output voltage to themotor; 2) the input frequency of VIN must match the frequency at theoutput of VSD 104; and 3) the voltage distortion present at the outputof the VSD 104 must be within a predetermined minimum level. The voltagedistortion requirement requires that an output L-C filter 404 must beintegrated into the VSD, to remove a majority of the output voltageharmonics from the VSD's output. It is also necessary that the controlscheme of the VSD 104 integrate two other features as follows: 1) outputcurrent-limiting control and 2) sensorless torque control. Outputcurrent-limiting control is configured to limit the available outputcurrent I_(VSD) to a predetermined limit. Sensorless motor torquecontrol is configured to control the motor torque using sensedparameters I_(MTR) and V_(MTR). To enable the VSD 104 to lock the outputvoltage in both phase and frequency to the AC input source 102, the ACinput source 102, or V_(IN), must be detected. Finally, the voltageV_(DC) at the DC link 204 is detected and controlled to a predeterminedvoltage level to enable the VSD 104 to adjust the RMS motor voltage tomatch the voltage VIN at the input to the VSD 104.

The system controls are usually implemented in the system control panel308. When the control panel 308 requires the compressor/motor 302, 106to operate within a prescribed range below the AC voltage sourcefrequency, the transition from VSD operation to bypass contactoroperation occurs. The range may be prescribed by plotting the efficiencyof the non-VSD equipped chiller against the VSD equipped chiller usingthe integrated part-load value (IPLV), which is a weighted average ofefficiency measurements at various part-load conditions, as described inARI Standard 550/590-98, and incorporated herein by reference. Thefrequency range is generally within 1.0 Hz of the maximum frequency. Forexample, for a 60 Hz line frequency, when operating at 59.0 Hz or above,more efficient operation is obtained by operating directly from the ACvoltage source 102. In one embodiment the transition to the bypasscontactor 400 does not occur until the system is operating in steadystate, e.g., an actual leaving chilled water temperature is within apredetermined band, e.g., plus or minus about 0.2° F., about a leavingchilled water temperature set point.

Referring to FIG. 11, control of the VSD 104 operation is described. Atstep 600, the control panel determines if the VSD frequency is greaterthan a pre-determined frequency, e.g., VSD frequency>59 HZ, for bypasscontactor operation. At step 610, a control signal is sent from thecontrol panel 308 to transition the operation of the VSD 104 from VSDoperation to full AC input voltage. At step 620, the output frequency ofthe VSD is controllably increased and the phase is adjusted to preciselymatch the AC voltage source frequency and phase. At step 630 the DC linkvoltage is adjusted as required to match the RMS motor voltage to theRMS input mains or AC voltage source voltage. At step 640, a currentlimit is enabled, and at step 650, the bypass contactor 400 is closed.At step 660 the gating signals for the inverter 206 and the activeconverter 202 are disabled. Although the inverter gating signals havebeen disabled, the DC Link voltage of the VSD remains at a level equalto approximately the peak of the input line to line mains voltage due tothe inverse parallel diodes contained within the inverter section 206.The operation of the inverse parallel diodes is set forth in greaterdetail in commonly owned U.S. Pat. No. 7,005,829, which is herebyincorporated by reference in its entirety. With both the inverter 206and active converter 202 gating signals disabled, the power dissipatedin the VSD 104 becomes essentially zero. Motor protection means, e.g.,motor overload current sensing, etc., is performed using the I_(MTR)parameter and motor disconnecting means, if required, can be implementedby disengaging the bypass contactor 400. The transition method justdescribed eliminates step changes in motor RMS voltage or motor RMScurrent, which in turn eliminates all torque transients and motor inrushcurrents caused by such step changes.

The reverse operation is set forth in FIG. 12. Transition from mainsoperation back to VSD operation should occur only when the systemcontrols require the compressor/motor 302, 106 to operate at a frequencywithin a prescribed range below the frequency of the AC input source102. In one embodiment, the prescribed range can be determined by theplotting the efficiency of the non-VSD-equipped compressor 302 againstthe VSD-equipped compressor 302 using the IPLV load line. In oneembodiment, the frequency range can be below 1.0 Hz of the maximumfrequency. When commanded to operate at 59.0 Hz or below, more efficientoperation of the system can be obtained by operating through the VSD104. In one embodiment, transition from bypass contactor 400 to VSD 104may occur only when the system is operating in steady state operatione.g., an actual leaving chilled water temperature is within apredetermined range (+/−0.2 F. degrees F.) about a leaving chilled watertemperature set point.

At step 700, the compressor/motor frequency f_(MTR) is compared with thefrequency of the AC input source 102, f_(AC INPUT), and if thedifference is greater than a predetermined amount, e.g., 1.0 Hz, at step705, the control panel sends a command signal to initiate transitionfrom full voltage of the AC input source, to VSD operation. Thetransition process commences at step 710 as follows. At step 710, theactive converter 202 is enabled and V_(DC LINK) is controlled to itsnominal set point. At step 720, the output frequency is set to thesensed input frequency of the AC input source 102, and the phase of theoutput voltage VMTR is set to the phase of the AC input source 102. Atstep 730, the current limit of the VSD 104 is enabled and the currentlimit level is set to equal the current level of the parameter I_(MTR).At step 740 the inverter gates are enabled and the DC link voltage isfinely tuned until the difference between the VSD current and the motorcurrent, i.e., parameter (I_(VSD)−I_(MTR))—is minimized. At step 750,the control system determines whether the parameter (I_(VSD)−I_(MTR)) iswithin a prescribed limit. If so, at step 760, the bypass contactor 400is opened and the VSD 104 powers the motor load. Otherwise, the controlsystem returns to monitor the difference (I_(VSD)−I_(MTR)).

Referring to FIG. 13, a modified reverse-blocking (RB) IGBT 450 is usedin each of the phases A, B and C, of the three-phase converter 202. Eachmodified RB IGBT 450 is formed by the inverse parallel connection of tworeverse-blocking IGBTs, in upper and lower switches, 450 a and 450 b,respectively. The modified RB IGBTs 450 are controllable to completelyextinguishing a ground fault. A diode 452 (see, e.g., FIG. 14) whichnormally provides a half wave conduction path around conventional orreverse-blocking IGBTs has been replaced with an anti-parallel IGBT 456.In order to ensure a complete disconnect of the VSD 104 from the motorload 106, bi-directional current flow must be extinguished in both theupper and lower portions 450 a, 450 b, of all three legs—A, B and C—ofthe active converter 202. While one phase leg of the active converterground fault protection is described, it will be understood by thosepersons skilled in the art that each phase of the active converteroperates in the same manner for multi-phase, e.g., three-phase, AC powersystems.

Each of the upper and lower switches 450 a and 450 b is comprised of twoRB IGBTs 454, 456. An RB IGBT is capable of blocking voltages in thereverse as well as the forward direction. A first RB IGBT 454 isconnected to an inverse or anti-parallel IGBT 456. The anti-parallelIGBT 456 is also an RB-type IGBT. The anti-parallel IGBT 456 can becontrolled, e.g., during a precharge operation of the DC link 204, topermit only small pulses of inrush current to reach the DC link 204.Further, the anti-parallel IGBT 456 can be controlled to conduct currentin one direction at all times, similar to the anti-parallel diode 452.The RB IGBT 454 blocks a positive emitter-to-collector voltage that isapproximately equal to the peak line-to-line voltage that appears acrossthe IGBT 454. The positive emitter-to-collector voltage remains blockedfor as long as the conduction of the anti-parallel IGBT 456 is delayedfor the purpose of precharge. Commonly assigned U.S. Pat. No. 7,005,829and U.S. Published Pat. App. No. 20060208685, No. 20060196203 & No.20050122752, disclose various means to implement an active convertermodule to allow for precharging the DC link of a VSD or a parallelactive harmonic filter, and the same are hereby incorporated byreference herein.

When a ground fault current is sensed by the VSD 104, both of the RBIGBTs 454, 456, in each power switch 450 are immediately turned off topreventing any current from conducting to the ground fault. The rapidswitching of the RB IGBTs 454, 456 extinguishes the ground fault currentin microseconds. By contrast, prior art circuit breaker mechanisms takeapproximately 40 milliseconds to interrupt the ground fault current.

Referring next to FIG. 14, a conventional 3-phase active convertermodule 440 includes a first RB IGBT 454 connected to an inverse oranti-parallel diode 452. The negative leg of the DC link 204 indicates aground fault condition 470. If all of the IGBTs 454 are gated off, acurrent path exists, as shown by broken line and arrow 472, when theinput voltage to the active converter is forward biased across diode452. Since the conventional diode 452 does not include a gate controlfor controlling current flow, the fault circuit is complete. Theconverter module 440 also includes the corresponding control connections(not shown) to control the switching of the power switches in a mannersimilar to the inverter module. As can be seen by comparing the circuitin FIG. 13 with the circuit shown in FIG. 14, the active converter 460shown in FIG. 13 has a controllable RB IGBT 456 connected inanti-parallel with the RB IGBT 454, rather than an anti-parallelconnected diode 452. The RB IGBT 456 enables the active converter 440 toessentially instantaneously open the faulted circuit and extinguish theground fault current, i.e., within microseconds. Thus, the amount oftime that the system components are exposed to damaging fault currentlevels is comparatively minimal.

The active converter 202 ground fault protection eliminates the need foran input circuit breaker equipped with ground fault protection, or withother electro-mechanical means to process the input power. The activeconverter 460 configuration allows for the use of power fuses ratherthan more costly circuit breakers to feed the power to the inputconverter of a VSD, while retaining the ground fault protection feature.Fuses provide a significant reduction in the let-thru energy associatedwith a line-to-line fault that may occur within the VSD or filter,thereby reducing instances of the semi-conductor package rupture, or ofother significant damage incurred in the case of a fault. By utilizinghigh speed fuses for the power feed, the arc-flash rating of theequipment (see, e.g., the National Fire and Protection Agency (NFPA)regulation 70E) can be significantly reduced. The high-speed fusesreduce the hazard associated with installing, maintaining and repairingthe system. By replacing main circuit breakers with fuses at the inputof the active inverter, the system can interrupt higher levels of faultcurrent, thus enabling the use of fused-input equipment on much lowerimpedance mains supplies. The active converter 460 significantly reducesthe energy associated with clearing the ground fault, becausesemiconductors and controls can detect and extinguish the ground currentflow in several microseconds, as contrasted with several millisecondsfor conventional topologies. The rapid response of the fuses minimizesancillary damage associated with a ground fault. This advantage may beparticularly apparent when used in HVAC&R applications where hermeticmotors are employed. A ground fault occurring in the stator winding of ahermetic motor can cause significant and costly damage to the entirerefrigeration circuit. Limiting the ground fault current that can flowin a stator limits collateral damage to other components of the HVAC&Rsystem.

Referring now to FIG. 15, a plastic cooler or cooling device 810 isdesigned to replace conventional copper heat sinks to provide cooling toa semiconductor module. While reference is made to semiconductor,SCR/Diode and insulated gate bipolar transistor (IGBT) modules, theplastic cooler 810 may be used with any suitable application wherecooling is needed. The plastic coolers 810 direct the flow of coolantfluid onto the IGBT in the semi-conductor module. The coolant fluid maybe any suitable fluid, e.g. water, glycol or refrigerant.

To facilitate full operation of the devices in the module, the coolersare capable of operating at a continuous use temperature ofapproximately 100 degrees centigrade and meet the UnderwritersLaboratory approval of plastic material for flammability according tothe appropriate standard (UL746A-E). The plastic material used for thecoolers 810 has a low level of liquid absorption, is physically durablewith a high tensile strength and may be injection molded or machined.Because the power assemblies in which the coolers 810 are mounted arecycled by both temperature and power, the plastic material must exhibita low temperature coefficient of thermal expansion to avoid wire bondbreakage within the semi-conductor module due to a mismatch ofcoefficient of thermal expansion between the plastic cooler and thecopper laminated structures attached to the semi-conductor power deviceterminals. Also, the plastic cooler 810 acts as a fastener to allow forthe attachment of multiple power devices together permitting a singlelaminated busbar structure to be used to for electrical connections,thereby allowing for a reduction in the size and weight of the overallpower assembly. While the plastic material can be obtained from multiplesources, one source for the material is known under the trade nameNoryl, Valox or Vespel.

One embodiment of the power assembly, shown in FIGS. 15-19, utilizes aplastic cooler 810 that directs coolant fluid onto the IGBT modules (notshown). The plastic coolers 810 are lighter than copper or aluminumbased heatsinks and are cheaper to manufacture and assemble. Further,the plastic coolers 810 are advantageous because they do not corrode ascoolant loops containing aluminum typically do over time. The plasticcoolers allow the IGBT power module's baseplate to operate at acontinuous use temperature of approximately 100 degrees centigrade. Theplastic cooler 10 may use any suitable liquid for cooling, e.g., wateror glycol.

The plastic cooler 810 is provided upon which an electronic component ormodule, including several high-speed switches, may be mounted. Theplastic cooler shown in FIG. 15 has mounting holes 811. These holes canbe designed to receive screws or bolts that engage the electroniccomponent and hold it in place. Although the plastic cooler is shownusing mounting holes to secure an electronic component to the baseplate, other fastening devices known in the art could be used to fastenthe electrical component to the plastic cooler. By means of exampleonly, the component can be fixed to or positioned on the plastic coolerby clamping devices, adhesives, welds, etc.

Machined or otherwise formed in plastic cooler 10 are two main fluidchannels 812 and 813, whereby a cooling fluid may be introduced into theplate via feed channel 812 and may exit the plate via drain channel 813.In the illustrated embodiment, these channels are relatively large,cylindrical channels that extend along the length of the plastic cooler810. The channels are sized and designed to have a relatively lowpressure drop along their lengths.

At the top of the plastic cooler are a series of concave wells 820. Inan exemplary embodiment, wells 820 are surrounded by an O-ring groove831 into which an O-ring may be placed. The electronic devices to becooled are then positioned in place over the wells and fastened viamounting holes 811, or other devices or means, whereby a watertight sealis created between the base of the device and the plastic cooler 810 viathe O-ring. There can be an individual well for each individualelectronic switch or device to be cooled, and the electronic device canbe positioned directly over the well, so that the electronic device'sbottom is placed in direct contact with the cooling fluid.

The wells can have a width and length, and shape, designed to match thewidth, length, and shape of the electronic component to be cooled. Forexample, in an HVAC application where the electronic components areswitches, the wells have a width of approximately 1.5 inches and alength of 3 inches. Cooling fluid enters a well from feed channel 812through an inlet port 821 formed in the well, flows through the well,and then exits out outlet port 822 and into outlet channel 813. Thesechannels in turn are connected to a heat exchanger for cooling thecooling fluid that exits channel 13.

The plastic cooler 10 and its components are designed to provide optimumheat transfer between the cooling fluid and the electronic components,in an efficient and cost effective manner. Optimum results are achievedwith wells having a depth within the range of 0.02 to 0.20 inches,coupled with a hydraulic diameter between 0.05 and 0.20, and with inletsthat are 90° nozzles, applying the cooling fluid at an angle ofapproximately 90° against the surface of the electronic component placedover the well. The hydraulic diameter of the wells is thus definedgenerally by the following equation: HydraulicDiameter=4×Cross-sectional area/(2×Well Depth+2×Well Width). The nozzlescan be located at the end of a well, as shown in the Figures, so thatthe cooling fluid in effect bounces off both the surface of theelectronic component and the walls of the well adjacent the nozzle.

The nozzles promote a high degree of turbulence due to the impingementof cooling fluid on the surface of the electronic component. Thisturbulence is sustained by the optimal selection of the well depth andhydraulic diameter. A shallower well depth or smaller hydraulic diameterwould tend to re-laminarize the flow, thereby decreasing some of theenhancement in heat transfer. On the other hand, a deeper well depth orlarger hydraulic diameter would tend to decrease the heat transferenhancement due to a reduction in the velocity of the fluid adjacent tothe surface.

The plastic cooler 810 and its components can be designed such that thepressure drop across the length of the inlet channel 812 issubstantially less than the pressure drop across the wells. The pressuredrop control in channel 812 can be achieved by increasing the size of atleast the inlet channel, relative to the size, shape, and flowcharacteristics of the well and its inlets and outlets. The pressuredrop across the length of inlet channel can be no greater than 1/10th ofthe pressure drop across the individual wells. In one embodiment, eachof the wells has the same size, shape, and fluid flow characteristics.

The inlets and outlets of the wells are in the form of elongated slots.These inlet slots have a width, length, and a depth. The resultant slotsare designed to serve as nozzles that direct cooling fluid against thebottom surface of the electronic components. Ports 821 and 822 aresufficiently small in comparison to channels 812 and 813 such that noappreciable pressure drop is measurable across the channel 813 ascooling liquid flows into each of the wells 820. As shown in FIG. 19,another embodiment of the inlet and outlet ports is shown whereby theinlet and outlet are actually a plurality of openings 825 formed intoeither end of the well 820.

The channels 812 and 813 are designed to provide substantially equalpressure along the entire length of both channels, with the result thateach well 820 “sees” the same inlet pressure and pressure differentialand is capable of having an equal flow and thus an equal coolingcapability. The use of channels having these desired characteristicsminimizes, and preferably avoids, the problem of reduced flow in eachsubsequent well that occurs in prior art devices.

As an example, when the wells have a width of approximately 1.291inches, a length of approximately 4.033 inches, and a depth ofapproximately 0.05 inches; and when the plastic cooler includes threewells, it has been found that channels 812 and 813 with a diameter of0.563 inches provides the desired flow and pressure dropcharacteristics. In that example, the ports 821 and 822 can extend alongsubstantially the entire width of the wells and the ports have a nozzlewidth of approximately 0.094 inches, a length of approximately 0.906inches, and a depth of at least 0.125 inches.

The ports can be formed as elongated slots that extend from the bottomof the well downward to the channels 812 and 813. These slots preferablyare perpendicular to the surface of the plastic cooler 810. This slotconfiguration achieves a more turbulent flow that enhances the heattransfer without significantly impacting pressure drop. Theuncomplicated shape of the wells, inlets and channels provides for mucheasier manufacturing than is associated with other related devices thathave wells of varying depths or require the use of obstacles placed inthe flow path to enhance the turbulent flow.

Also, by connecting each well 820 directly to the inlet 812 as opposedto having the cooling fluid flow in series from the first well to thelast, each well is fed with fresh coolant which maximizes the coolingcapability of all of the wells. Similar prior art devices utilize asingle path for the coolant such that by the time the coolant reachessubsequent wells, each prior well has transferred heat into the coolant.By the time the coolant reaches the last well in a series such as this,the cooling capability of the coolant is greatly diminished.

The power assembly may operate as single phase for applications thatrequire higher power output levels, or as three phases for applicationsrequiring lower power output levels. Referring now to FIG. 20, filmcapacitors 1500 are used in place of traditional electrolyticcapacitors. The use of a film capacitor 1500 reduces the cost ofmanufacture, reduces the total overall weight of the assembly, reducesthe overall size of the assembly, and increases the reliability of thesystem. The film capacitor 1500 increases the reliability of theassembly by eliminating the need to evaporate electrolyte liquid presentwhen the traditional electrolyte capacitors are used. Mounting apertures1504 are disposed or located on the capacitors 1500 for mounting othercomponents or subassemblies, e.g. bus plates 1506, angled bus plates1508, cooling devices 1512 and for attaching the assembly in a VSDenclosure (not shown). In addition, mounting bases 1510 are disposed orlocated on the film capacitor 1500 to mount the entire assembly on ashelf or other suitable surface (not shown). Fasteners 1516, e.g. screwsor other suitable fasteners, are used to mate with the apertures 1504 tosecure the components to the capacitor.

In another embodiment, additional electronic components can be affixedto the plastic cooler on the surface opposite the one with the openwells. Additional open wells are included on the opposite surface, andthe heat from the additional power devices is removed by the liquidcoolant in the plastic cooler that is in direct contact with the bottomof the device. The additional cooling wells provides cooling to thosecomponents in a fashion similar to prior art devices by transferring theheat through the component to the plastic cooler and then to the liquid,but adds the advantage of a very compact overall package.

Referring now to FIG. 21, inductor 400 can be composed of two majorsubassemblies—the core 402 and the coil 403. The core 402 subassembly iscomposed of a plurality of thin strips called laminations Multiplelamination sheets are stacked to form the core 402 of the inductor 400.During manufacture, silicon is added to the steel to improve theelectrical resistivity of the laminations 404. Grain orientation of thelaminations lowers the losses and extends the boundaries of usefuloperation of the core 402 material. Laminations are commonly used tominimize eddy currents and the losses associated with eddy currents,which become more of a concern as the operational frequency of theinductor rises. While silicon steel laminations will be referred tothroughout the application, it is known by those of ordinary skill inthe art that any type of suitable material may be used. Alternatematerials include but are not limited to nickel-iron, cobalt alloys,powdered iron, ferrous alloys, molybdenum permalloy powdered iron,nickel-iron powder, ceramic ferrites, manganese zinc ferrites, nickelzinc ferrites and manganese ferrites.

Core losses are caused by hysteresis losses and eddy current losses.Core losses increase the operating temperature of the core 402 andreduce the efficiency of the inductor 400. The operating temperature ofthe core 402 has an influence on the other materials used in theinductor 400, such as insulating materials and varnishes. Each materialhas a maximum operating temperature, and the operating temperature ofthe core 402 determines the available options for insulating materials.As the operating temperature increases the number of available optionsfor use as insulating materials is reduced, and the costs of thematerials is increased. The useful life of the inductor may also becompromised as the operating temperature of the inductor is increased.

The coil 403 subassembly can be composed of insulating materials andcurrent carrying conductors. The conductors may be any suitable type ofconductive material, e.g. copper and aluminum. Copper conductors have alower resistivity but a higher cost and weight than aluminum conductors.The sheets of the conductors are typically interleaved with layers ofinsulating material. The insulating material may be any suitableinsulating material e.g. Nomex, ceramic or woven glass fiber. Air ductsare provided between the coil layers to provide for the movement of air,either forced air or natural convection, which removes the heatgenerated by the losses associated with the coil. The operatingtemperature of the coil conductors and insulators is ultimatelydetermined by the combination of losses and air movement.

Referring to FIG. 22, the cooler (not shown) is applied to the topsurfaces of the core 602 of an inductor 600. The cooler 10 uses fluidsuch as water, glycol or refrigerant to cool the core 602. The fluidtravels through the cooler and absorbs the heat generated by the core.

To allow for heat conduction throughout the core 602 including the coregaps, a thermally conductive, non-ferromagnetic material 605 is used toprovide a proper magnetic gap, while also allowing for heat transferacross that gap. A material such as a “Grade A Solid Boron Nitride”material manufactured by Saint Gobain Ceramics can be used, however oneof ordinary skill in the art would know that any suitable type ofmaterial that is easily machinable and provides the necessary thermalconductivity may be used, e.g. aluminum nitride, ceramics manufacturedby ANCeram and alumina ceramics manufactured by Astro Met, Inc.

The coil 604 is formed by tightly interleaving layers of aluminum orcopper foil with layers of an electrically insulating and thermallyconductive material in order to form a low thermal impedance coilsubassembly. The heat generated at the coil subassembly is transferredby heat conduction from the coil 604 to the core and subsequently to theheatsink by where it is absorbed by the liquid flow. The electricallyinsulating but thermally conductive sheets of material are commonlyavailable e.g. Cho-Therm, Therma-Gap, Therm-Attach and Therma-Flowmaterials manufactured by Chomerics Inc., Sil-Pad and Gap-Padmanufactured by the Berquist Company and similar products produced byFujipoly Corp. One of ordinary skill in the art will appreciate that anysuitable materials that are compatible with the standard insulatingvarnishes used in conventional inductor manufacturing processes, andthat also exhibits tear-through capability with maximum continuous useoperating temperatures approaching 200 degrees Celsius may be used. Thecoil layers are tightly wound around the core leg to provide a thermallyconductive path to the core 602.

FIG. 23 shows the results of a computer simulation intended to predicttemperature distribution within the inductor 600 whose core 602 is shownin FIG. 22, by showing in shades of varying color, the thermal gradientwithin the inductor 600. Table 1 below shows the influence of variousthermally conductive, electrically insulating materials on the peakinductor temperature rise.

TABLE 1 Winding Material Aluminum Winding Thickness [in] 0.031 ThermalConductivity of 240 Winding Material [W/m-K] Heat Generation per coil[W] 1146 Heat Generation in the core 344 [W] Number of Winding Turns 15Gap Material Gap Pad 1500 Gap Pad 5000S35 Gap Pad 3000S30 Sil Pad 2000Gap Material Thickness [in] 0.03 0.02 0.01 0.01 Thermal Conductivity ofGap 1.5 5 3 3.5 Material [W/m-K] Overall wrapped winding 0.915 0.7650.615 0.615 thickness [in] Overall winding conductivity 3.03 12.35 11.8413.73 in transverse direction [W/m- K] Overall winding conductivity122.70 147.84 182.20 182.32 in parallel direction [W/m-K] MaximumTemperature Rise 290.4 233.8 232.4 229.0 [K]

Conductive connectors are placed between the IGBT and the laminatedcopper busbar to eliminate concerns with wire bond failures.

Another embodiment includes an active converter module with an integralmeans to control the pre-charging of the DC link capacitors in the powerassembly.

Referring next to FIG. 24, in one embodiment, a common mode capacitor 23is provided on differential mode filter 20 at an input to VSD 104.Differential mode filter 20 includes three capacitors 30 wye connectedbetween each of the three phases of three-phase input supply 102. Filter20 is wye-connected between the inductor tap portions 18. Groundingcapacitor 23 is connected to a common point 21 of filter 20. Earthconnection 22 is connected to the opposite terminal of capacitor 23 fromfilter 20. Grounding capacitor 23 on filter 20 provides more reliableoperation of VSD 104 when active converter modules 202 are used to powerDC link 204. For example, in case of common mode or line to grounddistortion present at the input of VSD 104. Distortion may be present ininput power source 102 due to other non linear loads operating on thesame power source 102, for example, another variable speed drive withactive front end converter modules.

Ground capacitor 23 with the input filter inductor 26, 28, provides afilter for the line to ground voltages, thereby reducing or eliminatingthe high frequency distortion across the input active power devices inconverter 202, e.g., IGBTs 451, or RB IGBTs 454, 456 (See, e.g., FIGS.13, 14).

Referring next to FIG. 25, a voltage waveform V_(lg) havinghigh-frequency distortion is shown. Waveform 250 shows line-to-groundvoltage V_(lg) when common mode input capacitor 23 is not present. Inthe example of FIG. 25, the high frequency distortion that is shown inthe voltage waveform is caused by another VSD connected to the sameinput power source 102.

FIG. 26 shows the line-to-ground voltage V_(lg) for the same VSD circuitas that of FIG. 25, modified to include common mode capacitor 23connected as shown in FIG. 24. Note that the high frequency noise in thevoltage waveform is significantly reduced.

While the exemplary embodiments illustrated in the figures and describedherein are presently preferred, it should be understood that theseembodiments are offered by way of example only. Accordingly, the presentapplication is not limited to a particular embodiment, but extends tovarious modifications that nevertheless fall within the scope of theappended claims. The order or sequence of any processes or method stepsmay be varied or re-sequenced according to alternative embodiments.

It is important to note that the construction and arrangement of thecommon mode and differential mode filter for variable speed drives, asshown in the various exemplary embodiments is illustrative only.Although only a few embodiments have been described in detail in thisdisclosure, those skilled in the art who review this disclosure willreadily appreciate that many modifications are possible (e.g.,variations in sizes, dimensions, structures, shapes and proportions ofthe various elements, values of parameters, mounting arrangements, useof materials, colors, orientations, etc.) without materially departingfrom the novel teachings and advantages of the subject matter recited inthe claims. For example, elements shown as integrally formed may beconstructed of multiple parts or elements, the position of elements maybe reversed or otherwise varied, and the nature or number of discreteelements or positions may be altered or varied. Accordingly, all suchmodifications are intended to be included within the scope of thepresent application. The order or sequence of any process or methodsteps may be varied or re-sequenced according to alternativeembodiments. In the claims, any means-plus-function clause is intendedto cover the structures described herein as performing the recitedfunction and not only structural equivalents but also equivalentstructures. Other substitutions, modifications, changes and omissionsmay be made in the design, operating conditions and arrangement of theexemplary embodiments without departing from the scope of the presentapplication.

1. A variable speed drive configured to receive an input AC power at a fixed AC input voltage magnitude and frequency and provide an output AC power at a variable voltage and variable frequency, the variable speed drive comprising: a converter connected to a three phase AC power source providing the input AC voltage, the converter being configured to convert the input AC voltage to a boosted DC voltage; a DC link connected to the converter, the DC link being configured to filter and store the boosted DC voltage from the converter; an inverter connected to the DC link, the inverter being configured to convert the boosted DC voltage from the DC link into the output AC power having the variable voltage and the variable frequency; and a filter comprising: a three-phase input capacitor bank comprising three capacitors connected in a wye configuration, each capacitor of the three capacitors being connected at a first end to one phase of the three phase AC power source and at a second end to a common point with the other two capacitors; a grounding capacitor connected between the common point and earth ground; and wherein the three-phase input capacitor bank is configured to filter line to ground voltages of the three phase AC power source to reduce or substantially eliminate high frequency distortion across the converter stage.
 2. The variable speed drive of claim 1, wherein the converter comprises active devices located at an input side of the converter.
 3. The variable speed drive of claim 1, further comprising a three-phase inductor, the three-phase inductor comprising a phase winding for each phase of the three phase AC power source, wherein each winding of the three-phase inductor having a center tap dividing each phase winding into a pair of inductor sections; and each of the three capacitors of the input capacitor bank being connected at the first end to a respective one of the center taps of the three phase induction.
 4. The variable speed drive of claim 3, wherein each of the pairs of inductor sections comprises a line side inductor and a load side inductor being connected at one end to the center tap, wherein the line side inductor being connected to the AC power source at a second end opposite the center tap, and the load side inductor being connected to the converter at a second end opposite the center tap.
 5. The variable speed drive of claim 1, further comprising a three-phase line reactor connected to the AC power source, the line reactor configured to limit an input current of the converter, to filter an input waveform and to attenuate electrical noise and harmonics associated with the variable speed drive.
 6. The variable speed drive of claim 1, further comprising an output filter connected at an output of the inverter, the output filter configured to filter the output waveform of the variable speed drive and to attenuate electrical noise and harmonics associated with the inverter.
 7. The variable speed drive of claim 6, wherein the converter further includes at least two semiconductor switches for each phase of the AC power source.
 8. The variable speed drive of claim 7, wherein each of the at least two semiconductor switches comprises a pair of reverse blocking IGBTs inversely connected in parallel.
 9. The variable speed drive of claim 8, wherein each semiconductor switch comprises an inverse parallel connection of the pair of the reverse blocking IGBTs.
 10. The variable speed drive of claim 9, wherein each of the reverse blocking IGBTs is controllable by a controller to completely extinguishing a ground fault current.
 11. The variable speed drive of claim 10, wherein the controller is configured to extinguish bi-directional current flow in a first semiconductor switch and a second semiconductor switch, for each of the three legs of the converter, to ensure a complete disconnect of the variable speed drive from a motor load connected to an output of the variable speed drive.
 12. The variable speed drive of claim 9, wherein one reverse blocking IGBT of the pair of reverse blocking IGBTs of each semiconductor switch is controlled to permit only small pulses of inrush current to reach the DC link.
 13. A filter for reducing or eliminating high frequency distortion of line to ground voltages in a variable speed drive, the filter comprising: a three-phase inductor having three windings, wherein each winding of the three-phase inductor further comprising a center tap, the center tap dividing each winding of the three-phase inductor into a pair of inductor sections; a three-phase capacitor bank having three capacitors connected in a wye configuration to the three center taps at one end, and to a common point at an opposite end; and a grounding capacitor connected between the common point and earth ground; wherein the three-phase capacitor bank is configured to filter line to ground voltages to substantially eliminate high frequency voltage transients across an input of a converter of a variable speed drive.
 14. The filter of claim 13, wherein each pair of inductor sections comprises a line side inductor portion and a load side inductor portion connected at one end to the center tap, and the line side inductor portion being connected to an AC power source at a second end opposite the center tap, and the load side inductor portion being connected to the converter of the variable speed drive at a second end opposite the center tap.
 15. The filter of claim 13, wherein the three-phase inductor is a five legged inductor comprising: a core element having at least three leg portions, each leg portion being wound with a pair of electric current carrying coils, and a flux portion, the flux portion connecting the at least three leg portions in a continuous magnetic path, the flux portion having a pair of vertical legs connected at a top end by a top leg and at a bottom end by a bottom leg to form a substantially rectangular frame portion, the three leg portions being positioned within and in magnetic communication with the frame portion.
 16. The filter of claim 13, wherein the three phase inductor is a four legged inductor, comprising: a core element having at least three leg portions, each leg portion being wound with a pair of electrical coils, and a flux portion, the flux portion connecting the three leg portions in a continuous magnetic path, the flux portion providing a common flux path, the flux path being excited by common mode current components flowing through the electrical coils.
 17. The filter of claim 13, wherein the filter is connected between an AC power source and the converter.
 18. The filter of claim 1, wherein the inverter is connected to an output capacitor bank of three capacitors, each capacitor connected in a wye configuration to an output phase of the inductor; each of the three capacitors of the output capacitor bank being connected in common at an end opposite the output phase connection; the common capacitor connection also being connected to earth.
 19. The filter of claim 1, further comprising: an output inductor having three output phase windings connected in series with the output phase of the inverter; and a second output capacitor bank of three capacitors, each capacitor of the second output capacitor bank being connected in a wye configuration to a load side of the output inductor; wherein currents induced by differential mode voltage components are removed from the load side of the output inductor and prevented from flowing to a load connected to the output inductor. 